1. The noradrenaline sensitivity of the isolated perfused rabbit artery was studied, during perfusion with Krebs solution, normal plasma, hypertensive plasma and a low-density lipoprotein (LDL) extract of normal plasma.
2. There was no difference in noradrenaline sensitivity between arteries perfused with Krebs and normal plasma.
3. Both hypertensive plasma and LDL potentiated the noradrenaline-induced vasoconstriction.
4. This potentiation was associated with increases in both the intrinsic activity of the drug-receptor complex and the drug—receptor affinity.
5. There is a circulating factor in the plasma of hypertensive patients which sensitizes arteries to noradrenaline, and this factor may be LDL.